A practical and economic way to produce filters is to use strings of melted glue on a filter media that is then folded so that the still melted glue fixes to the folds together prior to hardening. The melted glue simultaneously serves as distance elements and a fixture resulting in a filter matrix that then can be arranged in a frame to produce a filter. From EP 89850002.0, it is known to use intermittent strings to produce folded filters with folds having a very precise wedge shape to give optimal flow conditions. From EP 89850003.8 it is further known to use the very same glue strings that are used to hold the folds together to provide the folded filter matrix with a flat filter media membrane on the exit side. This promotes a very even flow from the filter and thus it can be used at clean room work stations.
Although the melted glue string filters have many good properties and enable practical fabrication solutions they are not free from drawbacks. One such drawback is that in reality it is not always easy to control the temperature conditions at all the individual nozzles for the melted glue. This means that the dispensed amount and its shape on the filter media will vary and thus the quality of the filter. A second drawback is that the glue strings have a rather limited span of dimension possibilities leading to an almost standardized size for the folds or distances between them. A third drawback is the cost. In a glue string filter matrix a major part of the cost is that of the glue. Also a major part of the material in filter will be the glue, which is a drawback at recycling and also from the point of fire conditions since the glue will easily burn even if the filter material is glass.
From the above it is apparent that further development would be welcome and needed.